Improvement of Power System Small-Signal Stability by Artificial Neural Network Based on Feedback Error Learning

Electrical power systems usually suffer from instabilities because of some disturbances occurring due to environmental conditions, system failures, and loading conditions. The most frequently encountered problem is the loss of synchronization between the rotor angle and the stator magnetic angle for synchronous generators. The contribution of this study is that a nonlinear adaptive control approach called feedback error learning (FEL) is utilized to improve the small-signal stabilities of an electric power system. The power system under study is composed of a synchronous machine connected to infinite bus. Many advantages of FEL control approach makes it capable to robustly adapting with all possible operating conditions rather than using optimization algorithms for tuning the conventional power system stabilizer (CPSS) that is still unsatisfactory especially at some critical operating points. The performances of two controllers, namely the proposed FEL scheme and the conventional controller CPSS, are tested by Matlab simulations. It is found that the FEL controller can be effectively used as an alternative stabilizer for improving small-signal stabilities of the powe

Electrowetting: from basics to applications

Electrowetting has become one of the most widely used tools for manipulating tiny amounts of liquids on surfaces. Applications range from 'lab-on-a-chip' devices to adjustable lenses and new kinds of electronic displays. In the present article, we review the recent progress in this rapidly growing field including both fundamental and applied aspects. We compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high. We discuss in detail the origin of the electrostatic forces that induce both contact angle reduction and the motion of entire droplets. We examine the limitations of the electrowetting equation and present a variety of recent extensions to the theory that account for distortions of the liquid surface due to local electric fields, for the finite penetration depth of electric fields into the liquid, as well as for finite conductivity effects in the presence of AC voltage. The most prominent failure of the electrowetting equation, namely the saturation of the contact angle at high voltage, is discussed in a separate section. Recent work in this direction indicates that a variety of distinct physical effects¿rather than a unique one¿are responsible for the saturation phenomenon, depending on experimental details. In the presence of suitable electrode patterns or topographic structures on the substrate surface, variations of the contact angle can give rise not only to continuous changes of the droplet shape, but also to discontinuous morphological transitions between distinct liquid morphologies. The dynamics of electrowetting are discussed briefly. Finally, we give an overview of recent work aimed at commercial applications, in particular in the fields of adjustable lenses, display technology, fibre optics, and biotechnology-related microfluidic devices

GREY WOLF OPTIMIZATION FOR POSITION CONTROL OF A DIRECT CURRENT MOTOR DRIVEN BY FEEDBACK LINEARIZATION METHOD

Several studies dealing with position control of the DC motor have reported issues concerning friction force. This article demonstrates a nonlinear control and optimization strategy for position control of a series servo motor. Once it is empirically verified that the linear model does not adequately reflect the system, the model is upgraded from linear to nonlinear. In the course of the research, the nonlinear feedback linearizing the controller's behavior is examined. A grey wolf metaheuristic optimization algorithm is used to find the coefficients of the controller's gains. In this way, modern methods are applied to take a fresh look at the existing problem. Furthermore, performance for various targeted output signals is compared to show the approach proposed in the study. Also, a compara- tive analysis with whale optimization algorithm is performed. The experimental results acquired on the stated system are shown, and they validate the usage of the nonlinear control, demonstrating the effectiveness of using optimum feedback linearization in electrical machines

Skin-Effect Self-Heating in Air-Suspended RF MEMS Transmission-Line Structures

Air-suspension of transmission-line structures using microelectromechanical systems (MEMS) technology provides the effective means to suppress substrate losses for radio-frequency (RF) signals. However, heating of these lines augmented by skin effects can be a major concern for RF MEMS reliability. To understand this phenomenon, a thermal energy transport model is developed in a simple analytical form. The model accounts for skin effects that cause Joule heating to be localized near the surface of the RF transmission line. Here, the model is validated through experimental data by measuring the temperature rise in an air-suspended MEMS coplanar waveguide (CPW). For this measurement, a new experimental methodology is also developed allowing direct current (dc) electrical resistance thermometry to be adopted in an RF setup. The modeling and experimental work presented in this paper allow us to provide design rules for preventing thermal and structural failures unique to the RF operation of suspended MEMS transmission-line components. For example, increasing the thickness from 1 to 3 mum for a typical transmission line design enhances power handling from 5 to 125 W at 20 GHz, 3.3 to 80 W at 50 GHz, and 2.3 to 56 W at 100 GHz (a 25-fold increase in RF power handling)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87277/4/Saitou15.pd

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 333)

This bibliography lists 122 reports, articles and other documents introduced into the NASA Scientific and Technical Information System during January, 1990. Subject coverage includes: aerospace medicine and psychology, life support systems and controlled environments, safety equipment, exobiology and extraterrestrial life, and flight crew behavior and performance

Measurement of the gradient of the Casimir force between a nonmagnetic sphere and a magnetic plate

We measured the gradient of the Casimir force between an Au sphere and a plate made of ferromagnetic metal (Ni). It is demonstrated that the magnetic properties influence the force magnitude. This opens prospective opportunities for the control of the Casimir force in nanotechnology and for obtaining Casimir repulsion by using ferromagnetic dielectrics.Comment: 15 pages, 4 figures, to appear in Phys. Rev.

Electron Beam Diagnostic at the ELBE Free Electron Laser

The radiation source ELBE is a scientific user facility able to generate electromagnetic radiation as well as beams of secondary particles. The figure below shows the layout of the facility. ELBE is based on a superconducting electron linac. The linac consists of two accelerating modules and uses TESLA type nine-cell niobium cavities, two cavities in each module. The cavities were developed at DESY in the framework of the TESLA linear collider project and the X-ray free electron laser (FEL) project. The ELBE linac is designed to operate with an accelerating field gradient of 10 MV/m so that the maximum design electron beam energy at the exit of the second module is 40 MeV. The essential difference of the ELBE linac from the future TESLA and X-ray FEL linacs is that ELBE operates in the continuous wave (CW) mode. ELBE delivers an electron beam with an average current of up to 1 mA. The electron source is a DC thermionic triode delivering beam with energy of 250 keV. The gun beam quality predefines the accelerated beam quality. One application of the electron beam is the generation of bremsstrahlung in the MeV energy range. The bremsstrahlung is used for nuclear spectroscopy experiments. Another application of the electron beam is the generation of quasi-monochromatic X-rays via channeling radiation in a single crystal. Thus X-rays with an energy from 10 keV through 100 keV can be generated. The channeling radiation is used for radio-biological and bio-medical experiments. In the future the ELBE electron beam will be used to produce monoenergetic positrons for material research. One more future application of the beam is the production of neutrons by bremsstrahlung via reactions. The neutrons will be used for material research oriented toward construction of future nuclear fusion reactors. In the author’s opinion, the most exciting and elegant application of the electron beam at ELBE is the infrared FEL. There are two FELs planned to run simultaneously at ELBE. The first one, with an undulator period of 27 mm, is going to operate in the wavelength range from 3 µm through 30 µm. The second one is in the design stage only but it will be built to work at longer wavelengths from 25 µm to 150 µm where the FEL has no competition from conventional quantum lasers. While an infrared FEL makes possible a great variety of experiments it is the device most sensitive to the electron beam quality. This dissertation is dedicated to the development of beam instrumentation and the measurement of electron beam parameters at ELBE. - In Chapter #1 we review fundamentals of FEL operation, discuss the importance of the electron beam quality for the FEL and lay down the requirements imposed by the FEL on the electron beam parameters. - Chapter #2 describes measurements of the transverse emittance we did at ELBE including an explanation of the experimental methods and the measurement error analysis. The transverse emittance was measured with the multislit method in the injector where the beam is space charge dominated. The transverse emittance of the accelerated beam was measured with the quadrupole scan method since the beam is emittance dominated. - Measurements of the electron bunch length, which is in the picosecond range, are described in Chapter #3. The bunch length was estimated from a frequency domain fit of a specially constructed analytical function to the measured power spectrum of the bunch. The power spectrum was obtained as a Fourier transform of the measured autocorrelation function of the coherent transition radiation (CTR). The CTR autocorrelation function was measured with the help of a Martin-Puplett interferometer. - A system of beam position monitors was designed, built, and commissioned in the framework of this effort. The design of our stripline BPM, the corresponding electronics and software is described in Chapter #4 along with the system performance as measured with the ELBE beam

Cost/benefit analysis of advanced materials technologies for future aircraft turbine engines

The materials technologies studied included thermal barrier coatings for turbine airfoils, turbine disks, cases, turbine vanes and engine and nacelle composite materials. The cost/benefit of each technology was determined in terms of Relative Value defined as change in return on investment times probability of success divided by development cost. A recommended final ranking of technologies was based primarily on consideration of Relative Values with secondary consideration given to changes in other economic parameters. Technologies showing the most promising cost/benefits were thermal barrier coated temperature nacelle/engine system composites